This invention relates generally to corona charger apparatus for use in electrostatographic reproduction devices, and more particularly to corona charger apparatus of simplified universal construction which can be used to accomplish any of various electrostatographic process steps requiring charge deposition.
In electrostatographic reproduction devices (copiers or copier/duplicators), a latent image charge pattern is formed on a dielectric support by altering a uniform electrostatic charge on the support in image-wise fashion corresPonding to information to be reproduced. Alteration of the uniform charge is accomplished, for example, by exposing a dielectric support including a photoconductive layer to a light image of information to be reproduced. Alternatively, alteration of the uniform charge may be accomplished by other well known methods such as exposure to electronically generated light signals.
After the latent image charge pattern is formed pigmented marking particles are attracted to the latent image charge pattern formed on the dielectric support to develop such image on the support. The dielectric support is then brought into contact with a receiver member and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support. After transfer, the receiver member bearing the transferred image is detached from the dielectric support and transported away from the support to a device where the image is fixed to the receiver member by heat and/or pressure to form a permanent reproduction thereon. As the image is being fixed on the receiver member, the dielectric support is cleaned of any residual marking particles and recharged for subsequent use.
It is common Practice in the described electrostatographic reproduction devices to use corona charger apparatus to provide an electrostatic field for the electrostatographic process steps requiring such fields. Particularly, such corona charger aPParatus may be used to deposit the uniform charge on the dielectric support, effect transfer of the marking particles of a developed image from the dielectric support to a receiver member, facilitate separation of the receiver member from the dielectric member after the parking particle transfer operation, and neutralize charge on the dielectric support to facilitate cleaning of the support.
Typical corona charger apparatus include a thin wire, fabricated of Tungsten for example, held at a high voltage to generate ions or charge current to charge a surface (dielectric support or receiver member) located closely adjacent to the charger apparatus. If desired, an electrically biased grid may be interposed between the wire and the surface to control the charge deposited on the surface. The corona wire is tightly suspended between two insulating blocks which also provide a support for a connection to a high voltage source. Tension in the corona wire must be accurately set to prevent undesirable sagging of the wire if the tension is insufficient or breakage of the wire if the tension is too high. Since the corona wire is thin, it is fragile and setting of the proper tension is difficult. Further, the corona wire may be partially surrounded by a shield. The shield may be electrically conductive or insulative, and may or may not have an electrical bias applied thereto. For example, the shield can be electrically conductive and held at ground potential in order to increase the charge current. As can be readily appreciated from the foregoing discussion, corona charger apparatus are of a somewhat diverse, comPlex and expensive construction.
While corona charger apparatus are noted for their ability to produce a relatively uniform charge deposit on a surface, the wire oF the charger apparatus deteriorates over time. Such deterioration results in non-uniformity of the charge deposit with a corresponding degradation of the information reproduced by the electrostatographic reproduction device. Accordingly, the corona charger apparatus must be periodically replaced to maintain high quality reproductions. Since as noted above such apparatus are of complex expensive construction, their replacement adds considerable expense to the upkeep and maintenance of electrostatographic reproduction devices. It has therefore been a desirable goal to provide a corona charger apparatus which is of simple, inexpensive construction so that it can be economically discarded when no longer useful for its intended function, and readily replaced by an unskilled operator. A recent corona charger apparatus addressing this desire is found in U.S. Pat. No. 4,754,305 (issued June 28, 1988, in the name of Fantuzzo, et al). The structure of this patent shows a corona charger aPparatus which has a throwaway subassembly. However, a portion of the apparatus remains in the reproduction device. Accordingly, only a partial reduction in complexity and expense of the corona charger apparatus has been achieved by this structure.